With the development of the display technology, due that flat display devices of liquid crystal displays (LCD) and the like have advantages of high definition, power saving, thin body, wide range application etc., the flat display devices are widely applied to various consumer electronic products of mobile phones, televisions, personal digital assistants, notebook computers, desktop computers and the like, so as to be the mainstream of the display devices.
Most of the liquid crystal devices in current market are backlight type liquid crystal display, which includes a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is: placing liquid crystal molecules in two parallel glass substrates, which have many vertical and horizontal fine wires between the two glass substrates; controlling the liquid crystal molecules to change direction by energizing or not energizing; and refracting light of the backlight module to produce frames.
Generally, the liquid crystal display panel is consisting of a color filter (CF) substrate, a thin film transistor (TFT) substrate, liquid crystal interposed between the CF substrate and the TFT substrate, and a sealant.
A thin film material is respectively formed on the CF substrate and the TFT substrate in the liquid crystal display, a main action of the thin film material is to arrange for the liquid crystal molecules according to a certain direction, the thin film material, we call an alignment film, usually is polyimide (PI) material. A main composition of this type alignment film is a rubbing alignment type PI material or an optical alignment type PI material; however, no matter what the type of alignment material is, it has its own shortcoming. Firstly, the rubbing alignment type PI material easily causes problems of dust particles, residual electrostatic, and brush mark etc.; thereby reducing process yield. Although the optical alignment PI material can obviate such problems, it has limited material characteristics, poor heat resistance, poor aging resistance, and weaker ability of anchoring liquid crystal molecules; thereby affecting panel quality. Secondly, the PI material itself has high polarity and high water absorption, storage and transport easily cause deterioration that results in uneven alignment, and the price of PI material is expensive, the process of forming a film on the TFT-LCD is complex; thereby increasing panel cost.
Additionally, the PI solution, used in fabricating the alignment film, contains a large amount of solvent N-methylpyrrolidone (NMP); therefore, the process of forming the alignment film is a high energy consuming, not environmentally friendly and human harmful process; moreover, due to the alignment film having issues of evenness, lack of coating, non-stick and foreign matter, the use of alignment film will result in product yield loss, resource waste, and product cost elevation. In the fabrication of liquid crystal display panel, if the arrangement of liquid crystal molecules is made by omitting the PI film, the cost of fabricating panels will be greatly reduced.